Numerous edible products, such as dairy products (e.g., yogurt, ice cream, cottage cheese, and the like), are packaged for retail sales in open-ended containers which are closed by a resealable lid. Resealable lids have for many years been employed in the food-packaging industry as a means to ensure that the consumer is provided with sanitary, unadulterated edible products. However, due to several well publicized criminal events that involved the intentional adulteration of packaged products, there has been an increased effort to provide enhanced tamperproof and/or tamper-evident packaging to supplement the protection which is afforded by resealable lids alone.
One proposal that has gained industry acceptance in terms of its enhanced tamperproof and/or tamper-evident functions is to heat-seal a film barrier of plastics material (preferably transparent) onto the upper circumferential edge of open-ended foodstuff containers. A resealable lid may then be placed onto the now film-sealed end of the container so that the lid/film seal collectively provide enhanced protection of the container contents. Moreover, a consumer may more easily be alerted to the possibility of the contents possibly being adulterated simply by visually inspecting the integrity of the film seal upon removal of the lid. If no visual evidence of film breakage, tearing or the like can be discerned, the consumer can have a greater level of confidence that the contained product will not have been illegally tampered with.
As can be appreciated, the advent of film seals in conjunction with conventional resealable lids has presented the packaging industry with special problems in terms of economically mass producing product-filled containers having both a heat-sealed film barrier and a conventional resealable lid. For example, U.S. Pat. Nos. 3,838,550 and 4,065,908 each issued to Martin Mueller, disclose heat-sealing a generally rectangularly shaped film barrier to the upper edge of open ended containers. The rectangularly shaped film barriers are, according to the techniques of the '550 Patent, preferably cut along mutually orthogonal longitudinal and latitudinal lines from a continuous web of film material. Once heat-sealed to the upper edge of the container, the four corners of the film extend below the upper container edge (see FIG. 1 in each of the '550 and '908 Patents) so as to provide gripping mechanisms which allow a consumer to more easily remove the film seal when access to the product contents is desired.
While the techniques disclosed in the '550 and '908 Patents certainly provide a measure of enhanced tamperproof and/or tamper-evident characteristics to the container, there are some improvements that could be made. For example, the rectangular configuration of the film necessarily forms four corners which, when applied to a generally cylindrical or slightly conical container, are each visible below the resealable lid (e.g., as shown in FIG. 1 in the '908 Patent). Visibility of the four corners on the exterior of the container may not always be aesthetically desirable and thus may detract from a consumer selecting a particular manufacturer's product in favor of a competitor's product.
One more aesthetically acceptable solution that has been proposed is to provide the film seal with a single tab element as represented by U.S. Pat. No. 4,176,507 to Derek V. Mancini. According to the technique disclosed in the '507 Patent, a preformed "daisy-chain" series of tabbed lids are fed to a heat-sealing station, where they are momentarily positioned in registry with an open end of a container (e.g., a single-serve condiment container), heat-sealed to the container end, and then severed from the adjacent tabbed lid. The resulting film-sealed container thus has an integral single tab which provides a consumer with a means to grip and remove the film so as to enjoy the contents of the container.
The technique disclosed in the '507 Patent, however, necessarily depends upon the formation and supply of an especially configured "daisy-chain" series of tabbed film lids. Thus, an especially adapted upstream fabrication apparatus which forms the series of such "daisy-chain" series of tabbed film lids from stock film sheets is needed, thereby increasing production costs.
It would therefore be highly desirable if standard film stock could be employed during packaging operations so as to produce economically product-filled containers with a heat-sealed barrier film cover having an integral pull tab. It is towards providing such a technique that the present invention is directed.
According to the present invention, methods and apparatus are provided for applying tamper-evident film seals onto the open ends of containers using a continuously advancing film stock. More particularly, the present invention provides packaging methods and apparatus which simultaneously heat-seals a film to a container and then circumferentially cuts the film around the container's upper edge. As a result, the perimeter of the heat-sealed film closely conforms to the circumferential geometry of the open container end.
The circumferential cut is performed using a cam-articulated orbiting cutting blade. The orbital path of the cutting blade around the circumference of the container's upper edge (i.e., an orbit about the longutidinal central axis of the container) is controlled by a camming mechanism which preferably forms a generally elliptical protrusion near the end of the blade's orbit. This protrusion thus forms a convenient pull tab for the tamper-evident film which more easily permits a consumer to access the container's contents.
The film stock is advanced into registry with the containers using a novel film-advancing system according to the present invention. In this regard, the film stock is supplied to a heat-sealing station by means of a continuously driven supply roll. On the other hand, the waste film (e.g., the webbing that remains after removal of the tamper-evident film seals) is taken up by means of a continuously driven take-up roll.
Discrete sections of the supplied film stock are synchronously indexed with an advancing group of containers by means of a dancer roll system which serves as a mechanical buffer between the continuously advancing film stock from the supply roll and the continuously retreating waste web onto the take-up roll. That is, the continuously advancing film stock is temporarily accommodated by means of a substantially horizontally moving supply dancer roll which essentially allows the advancing film to accumulate. At the same time, however, previously accumulated waste film webbing is continuously being paid-out at the same rate by means of a substantially horizontally moving discharge dancer roll. The net effect of these dancer rolls is to allow a length of film stock therebetween to be stopped momentarily in a registered positioned above a stationary set of open containers that have been indexed into position. During this momentary stoppage, the heat sealing and film-cutting functions can be accomplished, after which the now heat-sealed containers are advanced and the cycle repeats itself.
Thus, the present invention provides economical techniques for providing open-ended product-filled containers with heat-sealed film covers that are well suited for implementation on a mass production scale. Further aspects and advantages of this invention will, however, become more clear after careful consideration is given to the detailed description of the preferred exemplary embodiments which follow.